1. Field of the Invention
The invention relates to a torsion wrench, more particularly to a torsion wrench with a display unit for displaying the torsion force limit thereon.
2. Description of the Related Art
When manipulating a torsion wrench to tighten or loosen a workpiece, the operator easily overtightens or fails to tighten sufficiently the workpiece because an improper torsion force was applied on the workpiece. In order to overcome this drawback, there is a conventional torsion wrench which can be adjusted so as to generate an alarm sound when a predetermined torsion force limit is reached. The conventional torsion wrench 10, as shown in FIG. 1, includes a tubular casing 11, a drive unit 13, a knocker 15, a biasing member 16, and an adjusting unit 14. The drive unit 13 has a head portion 130 that is adapted to engage a workpiece (not shown), and a shaft portion 131 that extends into the casing 11 and that is mounted pivotally to a first end of the casing 11 by means of a pin 12. The knocker 15 is disposed in the casing 11 and is connected to a distal end of the shaft portion 131. The knocker 15 knocks on the casing 11 so as to generate an alarm sound when the torsion force that is applied by the drive unit 13 on the workpiece reaches a predetermined torsion force limit. The biasing member 16 is disposed in the casing 11 and biases the knocker 15 toward the shaft portion 131 to prevent the knocker 15 from knocking on the casing 11 when the torsion force that is applied by the drive unit 13 has not yet reached the predetermined torsion force limit. The adjusting unit 14 is used to adjust an initial biasing force that is applied by the biasing member 16 on the knocker 15 so as to correspond with the predetermined torsion force limit. The adjusting unit 14 includes a push rod 142 mounted movably in the casing 11 and abutting against the biasing member 16, a tubular handle member 141 sleeved rotatably on a second end of the casing 11 and connected operably to the push rod 142, and a locking unit 144 for locking the handle member 141.
In use, the handle member 141 is rotated to cause axial movement of the push rod 142 in the casing 11 so as to adjust the initial biasing force of the biasing member 16 to correspond with the predetermined torsion force limit. The locking unit 144 is then operated to lock the handle member 141 in order to maintain the initial biasing force at an amount corresponding to the predetermined torsion force limit. When the torsion force that is applied by the drive unit 13 on a workpiece reaches the predetermined torsion force limit, the knocker 15 separates from the distal end of the shaft portion 131 to knock on the casing 11, thereby generating an alarm sound.
When setting the torsion force limit in the conventional torsion wrench 10, the handle member 141 is rotated so that graduations on the handle member 141 are aligned with corresponding graduations on the casing 11. Since the graduations are very small, setting and reading of the torsion force limit in the conventional torsion wrench 10 is inconvenient to conduct.